1. Field of the Invention
The present invention relates to a medical image display apparatus, a medical image display method and a medical image display program for displaying two images in such a manner that comparative image reading on regions of interest in the two images is possible when the two images have been obtained by imaging a same subject at different points in time.
2. Description of the Related Art
In image-based diagnosis using two three-dimensional images obtained by imaging a same subject at different points in time by using same or different imaging apparatuses (modalities), a non-rigid registration technique has been drawing attention. In the non-rigid registration technique, a transformation function that matches the spatial positions of the subject in the two images with each other when the two images are placed one on the other is estimated, and the positions of the two kinds of image are matched with each other by deforming one of the images by using the estimated transformation function. In this non-rigid registration technique, control points for dividing image space at predetermined intervals are set. Then, deformation amounts of the control points that maximize an evaluation function for evaluating the similarity of voxel values between one of the images that is deformed by displacing the positions of the control points and the other image are determined. The transformation function is estimated based on the deformation amount of the control point at this time.
Japanese Unexamined Patent Publication No. 2011-092677 (Patent Document 1), PCT Japanese Publication No. 2009-522005 (Patent Document 2) and Japanese Unexamined Patent Publication No. 2008-086400 (Patent Document 3) present medical image display methods in comparative display of medical images representing an organ at plural points in time. In the methods, a region of interest in a medical image at a point in time corresponding to a region of interest in a medical image at a different point in time is identified by using the non-rigid registration technique. Further, one of the medical images is deformed so that the medical images representing the organ at plural points in time match with each other. A medical image that represents a region of interest at a point in time and a medical image that corresponds to this medical image and represents a region of interest at a different point in time (an image deformed to match medical images representing the organ at different points in time with each other) are displayed in such a manner to be comparable with each other. Further, Japanese Unexamined Patent Publication No. 2009-195306 (Patent Document 4) presents a medical image display method in comparative display of medical images representing bronchi at plural points in time. In the method, a corresponding landmark (a branching region in the bronchi) is extracted from each of the medical images, and a coordinate transformation parameter for matching the corresponding landmarks with each other is calculated by using a linear optimization technique. A medical image representing a region of interest at a point in time and a medical image that corresponds to this medical image and represents a region of interest at a different point (an image generated by performing coordinate transformation using the coordinate transformation parameter) are displayed, based on the calculated coordinate transformation parameter, in such a manner to be comparable with each other.